Photographic stencil particularly for diffusion printing



Feb. 15s; 1958 c. ECKARDT 2,824,000 PHOTOGRAPHIC STENCIL PARTICULARLY FOR DIFFUSION PRINTING Filed Dec. 4, 1952 MATERIAL FROM THE GROUP CONSISTING. OF CH WATER-SOLUBLE LAYER OF WAX, GUM .ARABIO, AND A SOF'T'ENEFL BACKING OF YOSHINO PAPER.

United States Patent PHOTOGRAPHIC STENCIL PARTICULARLY FOR DIFFUSION PRINTING Curt Eckardt, Nieder-Beerbach-Darmstadt, Germany Application December 4, 1952, Serial No. 324,135 Claims priority, application Germany December 6, 1951 2 Claims. (Cl. 96--75) This invention relates to a photographic stencil particularly for diffusion printing.

Photographic stencils for the preparation of photographic prints in the duplicating industry are generally known. These stencils are generally prepared with gelatine-glue or albumin-bichromate layers, but are not really suitable as marketable products, since they have a W stability in storage and are difficult to deal with in the hands of unskilled persons. Moreover, the layers impervious to ink readily become porous during their further working up, so that blurred copies are obtained. These stencils cannot be employed for diffusion printing on letter-press machines, since most of the oil-soluble and fat-soluble printing inks penetrate through the entire stencil after a short time. Moreover, such photographic stencils have no diffusion layer which first absorbs the ink and then passes it on to the printing paper under the presure of the printing machine.

The invention relates to a photographic stencil which is suitable more particularly for diffusion printing and is stable on storage and can readily be handled.

According to the invention, as illustrated in the sole figure, the photographic stencil comprises a backing of fibrous material, such as Yoshino paper, a diffusion layer consisting of a mixture of wax rendered water-soluble by means of protective colloids, soft resins and plasticisers, an intermediate layer impervious to ink but readily soluble in water, consisting of wax and soft resins and a covering layer of hard resins, such for example as shellac or sandarac resin, which have been rendered water-soluble by means of protective colloids and sensitized by the addition of light-sensitive substances, such as silver salts or bichromate salts, diazo dyestuffs or the like.

These substances harden on exposure to light and then form water-insoluble parts at those points of the stencil on which the light impinges. Thus, if the stencil is introduced into a water bath after exposure to light, the water-soluble parts of the light-sensitive points and those points of the intermediate layer which are situated therebelow are washed out, so that the ink can pass through these points to the dilfusion layer and can be absorbed thereby.

Since the substances employed for the intermediate layer harden and become water-insoluble in light after sensitisation with light-sensitive substances, all the layers can also be sensitised. A mixture of emulsions of soft resin, wax and hard resin can then also be employed for the covering layer. These sensitised emulsions can also be combined with albumin emulsions or gelatine emulsions.

The printing emulsions can be employed both for the positive process and for the negative process so that there are new possibilities not only for stencil printing, but also for offset and intaglio printing and for the manufacture of printing blocks.

If only the covering layer is sensitised, the various layers can be given substantially the following composition:

Diffusion layer:

50 parts of wax emulsion 30 parts of gum arabic solution 5 parts of glycerin The fibrous materialis while floating thereon.

Intermediate layer:

50 parts of wax emulsion 50 parts of gum arabic solution The fibrous material is again coated therewith after drying of the first layer.

Covering layer:

50 parts of shellac emulsion 10 parts of ammonium bichromate solution Example I saturated with the emulsion Diffusion layer:

50 parts of wax emulsion 30 parts of gum arabic solution 5 parts of glycerin 10 parts of bichromate solution The fibrous substance is saturated therewith while floating thereon.

Intermediate layer:

50 parts of wax emulsion 50 parts of gum arabic solution 5 parts of glycerin 15 parts of bichromate After the drying of the first layer, the fibrous substance is saturated therewith.

Covering layer:

50 parts of shellac emulsion 30 parts of wax emulsion 20 parts of gum arabic solution 15 parts of bichromate solution The fibrous material is then coated with the covering layer on both sides.

Example II be replaced by gelatine.

3 including wax, gum arabic, and a softener, a cover layer arranged on said intermediate layer opposite to said diffusion layer, said cover layer consisting of a third emulsion including wax and a substance selected from the group consisting of shellac and sandarac gum, a protective colloid selected from the group consisting of gum arabic, albumin and gelatin, said protective colloid being added to said emulsions so as to render the same water-soluble, and a light-sensitive substance selected from the group consisting of chromium salts, silver salts, and diazo compounds and added at least to said covering layer whereby said light-sensitive substance hardens 4 upon exposure to light, whereas said layers may be washed out at the non-exposed parts thereof.

2. Photographic stencil as claimed in claim 1, said light-sensitive substance being added to said diifusion and intermediate layers in addition to said cover layer.

Pin May 30, 1916 Albers et al. May 11, 1943 

1. PHOTOGRAPHIC STENCIL FOR DIFFUSION PRINTING, COMPRISING, IN COMBINATION, A BACKING CONSISTING SUBSTANTIALLY OF YOSHINO PAPER, A DIFFUSION LAYER ON SAID BACKING, SAID DIFFUSION LAYER CONSISTING OF A FIRST EMULSION INCLUDING WAX, GUM ARABIC, AND A SOFTENER, AN INTERMEDIATE LAYER ARRANGED ON SAID DIFFUSION LAYER OPPOSITE TO SAID BACKING, SAID INTERMEDIATE LAYER CONSISTING OF A SECOND EMULSION INCLUDING WAX, GUM ARABIC, AND A SOFTENER, A COVER LAYER ARRANGED ON SAID INTERMEDIATE LAYER OPPOSITE TO SAID DIFFUSION LAYER, SAID COVER LAYER CONSISTING OF A THIRD EMULSION INCLUDING WAX AND A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF SHELLAC AND SANDARAC GUM, A PROTECTIVE COLLOID SELECTED FROM THE GROUP CONSISTING OF GUM ARABIC, ALBUMIN AND GELATIN, SAID PROTECTIVE COLLOID BEING ADDED TO SAID EMULSIONS SO AS TO RENDER THE SAME WATER-SOLUBLE, AND A LIGHT-SENSITIVE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CHROMIUM SALTS, SILVER SALTS, AND DIAZO COMPOUNDS AND ADDED TO AT LEAST TO SAID COVERING LAYER WHEREBY SAID LIGHT-SENSITIVE SUBSTANCE HARDENS UPON EXPOSURE TO LIGHT, WHEREAS SAID LAYERS MAY BE WASHED OUT AT THE NON-EXPOSED PARTS THEREOF. 